An ion guide is widely used in transporting ions in a mass spectrometer. In PTL 1, a multipole ion guide configured of parallel rod electrodes of a multipole (quadrupole, hexapole, octupole, or the like), is disclosed. In PTL 2, an ion guide in which ions move between the ion guides by climbing over a pseudopotential barrier between two ion guides by a DC potential, is disclosed. In PTL 3, an ion guide which forms one multipole ion guide by combining two independent multipole ion guides, is disclosed.